1. Field of the Invention
The present invention relates to a chemical intermediate having the following structure (I): ##STR1## This diol can be used as a monomer for the preparation of water absorbent polyethers and polyesters.
2. Description of the Prior Art
In the past, many attempts have been made to employ carbohydrates for the development of well-characterized novel polymers of some practical significance. The use of sugars and their derivatives in the production of polymers is of growing interest since polymers containing mono- or disaccharides in their main chain or as grafted pendant groups or chains display useful and unique properties such as hydrophilicity, chirality, biological activity, biodegradability, and the like. Furthermore, most sugars are available at economical prices and are industrially produced in large quantities by cultivation in plants and microorganisms, followed by chemical isolation or by degradation of plant waste material followed by isolation. For instance, sucrose is produced on a scale that is larger than any other pure organic chemical, world-wide.
The major problem associated with the use of carbohydrates for developing polymers is the similar reactivity of the primary and secondary hydroxyl groups on the carbohydrate moiety. Hence, when carbohydrates are polymerized non-enzymatically with other monomers, the resulting polymer products are often a mixture of linear, cross-linked and branched chain products. This is due to the reaction of both the primary and secondary hydroxyl groups in the carbohydrate moiety with electrophilic groups in the other monomer.
Many attempts have been made in the past towards polymerizing carbohydrates such as those attempts described by N. Ogata et al in J. Polym. Sci., Polym. Chem. Ed., Vol. 19, p. 2609 (1981) and Vol. 22, p. 739 (1984); and S. K. Dirlikov, "Monomers and Polymers Based on Mono and Disaccharides", Pacific Polymer Preprints, First Pacific Polymer Conference, December 12-15, 1989, Volume 1, pp. 113-114.
Although Dirlikov, supra, claims that high molecular weight polymers have been made, no proof has been shown that these polymers are strictly linear and do not contain additional cross-linked or branched chain polymers and that only the primary hydroxyl groups react thereby forming a strictly linear polymer.
Sucrose used as a starting carbohydrate for the production of carbohydrate polymers would be ideal since it is produced in vast quantities and is low in price. To synthesize intermediate sucrose derivatives for further use in the production of novel polymers using sucrose as a starting compound is difficult due to the reactivity of the primary hydroxyl groups at carbons 6, 1' and 6' and the remaining five secondary hydroxyl groups.
For instance, U.S. Pat. No. 4,156,776 describes a 1',2,3,3',4',640 -hexa-O-acetylsucrose derivative that is useful as a component of inks, adhesives, coatings and vinyl ethers, but this compound contains acetyl moieties as does the acetoxy derivative of 4,6-O-isopropylidene sucrose a potentially useful synthetic intermediate. The use of acetates as semipermanent protection of secondary hydroxyl groups is often unfeasible since the hydroxyl group at the 6 position undergoes an internal acetate exchange to produce the 6-acetate and an hydroxyl group at the 4-position. In addition when acetates are used to protect secondary alcohols, the acetate protecting groups preclude the use of bases or nucleophiles in their presence.
Protecting the secondary hydroxyl groups in tri-O-trityl sucrose as the methyl ethers followed by reductive cleavage of the trityl groups affords an intermediate 2,3,3',4,4'-penta-O-methylsucrose. This compound is further manipulated to prepare 1',2,3,3',4,4'-hexa-O-methylsucrose as well as many other monomers.
It has now surprisingly been discovered that the diol monomer of 1',2,3,3',4,4'-hexa-O-methylsucrose can be synthesized via a two step process from 6,6'-dichloro-6,6'-dideoxy-1',2,3,3',4,4'-hexa-O-methylsucrose and that this compound can be used for the preparation of water absorbent polyethers and polyesters.